The invention relates to a snare instrument with a snare structure which is formed in one piece from a tube section, by the latter being slit and bent open, and which has a proximal base portion and, extending axially forward from the latter, a distal snaring portion, and which is movable between a snaring position, in which it is moved forward out of an enclosure with the snaring portion folded open, and a securing position, in which it is moved back at least partially into the enclosure with the snaring portion folded in and providing a securing action. Snare instruments of this kind are used in particular as medical snare instruments in order to be able to catch and remove foreign bodies, blood clots, stones or other concretions from human or animal tissues, preferably using a corresponding catheter instrument.
In a known type of instrument of this kind, the folded-open snaring portion has a basket shape, i.e. it forms a snaring basket which, in the folded-up state, is received in the enclosure, and which can be moved forward out of the latter, as a result of which it unfolds into its basket shape. Stones and the like can then be maneuvered into the wire basket, transversely with respect to the longitudinal axis thereof, in the area of its maximum diameter and, consequently, maximum opening width. The reason is that, in this area, adjacent wire sections of the basket-forming snare structure are at their maximum spacing, as a result of which corresponding snare openings are formed there on the circumference of the basket. By pulling the wire basket at least partially back into the enclosure, said wire basket is folded inward until it tightly encloses the snared object and thereby secures the latter. The wire basket and the enclosure, along with the snared object, can then be moved out of the tissue channel in question. Stone-collecting basket instruments and balloon catheter instruments of this kind are disclosed, for example, in the patent specification EP 1 809 187 B1 and in the laid-open publication DE 197 22 429 A1.
Another known type of snare instrument of this kind is what is called a snare loop instrument, in which the snare structure is formed from one or more interacting wire loops which can be loose or fixed at the front; see, for example, the laid-open publication WO 02/078632 A2.
The laid-open publication US 2005/0165442 A1 discloses a filter wire structure which is designed to be placed permanently in a tissue channel, in particular in a blood vessel, in order to catch particles or blood clots and thereby prevent embolisms. The filter wire structure is formed in one piece from a tube section, by the latter being slit and bent open, and has a cup shape which terminates at the distal end with V-shaped tips that face forward and slightly radially outward. These distal cup ends, tapering in a V-shape, result from the associated special slitting of the tube section in its outermost distal end portion. Open axial slits introduced from the direction of the distal end of the tube section alternate with closed axial slits which lie between the open axial slits and which terminate at a distance in front of the distal end of the tube section, wherein the open and the closed axial slits, in an axially overlapping area, are about the same width and considerably narrower than the wire sections thus formed between the slits from the tube section. At the distal end, the open slits extend forward with conical widening, such that the radius of an area of curvature, via which in each case two of the wire sections are joined together at the distal end, is at most approximately as large as the width of the wire sections there. The forwardly tapering V-shape of these wire section connections is thus retained even after the filter wire structure has been bent open.
It is an object of the invention to provide a snare instrument which is of the type mentioned at the outset and which offers a good snaring function and a high degree of functional reliability and can be produced with relatively little outlay.
The invention achieves this object by providing a snare instrument comprising a snare structure which is formed in one piece from a tube section, by the latter being slit and bent open, and which has a proximal base portion and, extending axially forward from the latter, a distal snaring portion, and which is movable between a snaring position, in which it is moved forward out of an enclosure with the snaring portion folded open, and a securing position, in which it is moved back at least partially into the enclosure with the snaring portion folded in and providing a securing action. In this snare instrument, the snaring portion, in the folded-open state, has a cup shape with a distal snare opening. Here, a snare opening is to be understood as the area of the maximum opening width of the snare structure, which area is intended and designed to allow objects snared therethrough to pass into the interior of the snare structure. For this purpose, a distal end area of the tube section, which is used to produce the snare structure, is provided with open axial slits of suitable length introduced from the direction of the end of the tube section, and, lying between these, with closed axial slits which terminate at a distance in front of the distal end of the tube section, wherein the closed axial slits are of greater length than the open axial slits and therefore extend in the proximal direction beyond the open axial slits. The remaining tube section areas between the open and closed axial slits form wire sections which, by means of the tube section being bent open, form circumferential portions of the snare opening. When necessary, the snaring portion can be fully folded inward or contracted from its folded-open, cup-shaped state back to a shape corresponding to the tube section when the snare structure is moved completely back into the enclosure.
With the snare instrument according to the invention, stones or other particles in body tissues can be advantageously snared from the front, i.e. they pass from the front in the axial direction through the distal snare opening into the snaring portion that has folded out into a cup shape. For this purpose, the snare structure can be correspondingly moved axially forward. In this way, particles located in the distal direction near a vessel wall can also be snared without any problem. The instrument according to the invention can also be used in the manner of a filter or stent to snare and remove foreign bodies from blood streams and other vessels of the body.
The snare instrument according to the invention can be produced with relatively little outlay since its snare structure is formed in one piece from a tube section which, for this purpose, is slit and bent open in a manner known per se. Welding points for the connection of wire sections can be dispensed with. Since the slits opening out at the distal end of the tube section have a suitable length, the wire sections, which are formed from the tube section by the open and closed axial slits in the axial overlapping area thereof, can form the circumference of the snare opening, i.e. the distal edge of the cup structure of the folded-open snaring portion. Thus, the circumferential length and therefore also the snaring cross section or opening width of the snaring cup can be predefined by the length of the open axial slits. With a greater length of the open axial slits, the circumferential length and therefore the snaring cross section of the snaring cup can be increased. Since the closed axial slits extend proximally beyond the open axial slits, they divide the tube section, in the proximal area behind the open axial slits, into rear wire sections which, in the folded-open state, form a cup body for the snaring cup, and, as has been mentioned, this cup body, at its distal end, terminates with the cup edge formed by the front wire sections. Each rear wire section thus branches into two front wire sections.
In a development of the invention, two adjacent front wire sections, formed from the tube section by the open and closed axial slits, are in each case joined together via an area of curvature, of which the radius RD is at least as great as two and a half times a width bD of the wire sections in the area of curvature, i.e. RD≥2.5×bD. It has been found that, with this dimensioning, the wire sections are able to bend open very advantageously to form the cup edge, without any danger of breaking, wherein edge areas of the cup tapering to a tip that could cause risks of tissue injury during use are avoided.
In a development of the invention, a circumferential length U of the snare opening is 70% or more of the product of the number 2n of the wire sections formed from the tube section by the open and closed axial slits, multiplied by the length L of the open axial slits, i.e. U≥0.7×2 nL. This dimensioning permits the provision of a comparatively large snaring cross section with a cup edge which, in the axial direction, has V-shaped portions with obtuse angles and not acute angles.
Depending on the bending-open process used, it is possible, in a development of the invention, to obtain different cup shapes of the snaring portion in the folded-open state, with areas in which the cup diameter increases linearly, progressively or degressively in the distal direction.
In a development of the invention, a maximum cross section of the cup shape of the snaring portion in the folded-open state is greater than a cross section of the snare opening. In certain applications, this can make it easier to secure a snared particle in the snaring cup that has been folded inward.
In a development of the invention, the snaring portion comprises further, second closed axial slits in the tube section, which slits extend forward with their distal end at the level between a distal and a proximal end of the first closed axial slits and rearward with their proximal end behind the proximal end of the first closed axial slits. This permits a wire-branching configuration of the cup body formed in this case by the first and second closed axial slits.
In a development of the invention, the snare structure and/or the enclosure and/or a pulling wire guided axially movably in the enclosure for the snare structure is provided across the whole surface or a partial surface, or at points, with a magnetic resonance (MR) marker material. This permits an advantageous use of the snare instrument in corresponding MR applications, since its snare structure is visible under MR.